It is the purpose of this invention to provide an improved apparatus, system and method for verifying the accuracy of printed and other reproduced material. In particular, this invention is especially applicable for determining the accuracy of printed material employed for data storage and similar technologically demanding applications. Several particular applications of the invention in the field of data recording and retrieval will be described in detail.
One difficult task frequently encountered in the field of data recording, particularly in the retail sales industry, is the rapid identification of a large number of items. In retail grocery stores, for example, there is a large cost associated with charging or "checking out" retail sale items correctly and expeditiously. When reading price labels, clerks frequently make mistakes, or if a price label on an item is lost, a substantial amount of time is wasted ascetaining the correct price.
In response to this problem, the retail sales industry has accepted and has begun using successfully for some time a manner of identifying items with a Universal Product Code (UPC). This code can be automatically read by an optical scanner. These codes are now being used in supermarkets and other retail areas, although their use is not limited to the retail field. For example, such codes can be used to identify blood samples, library books or the like.
As a supermarket clerk is checking out an item, the Universal Product Code printed on the item is moved relatively to an optical scanner that emits a beam of light and records the reflectance of portions of the Universal Product Code. From its pattern of reflectance, the scanner can read the imprinted code. The scanner is usually equipped with a memory so that it can compare the identified code with items of stored information. One piece of stored information would usually be the price of the item. In addition to storing a price record of the item, the scanner can also keep a record of each item that is purchased, with the aim of keeping an accurate control over inventory.
Since the adoption of the Universal Product Code, more and more businesses are using them, and they are generally credited with saving a great deal of time and expense in the retail field.
The printed Universal Product Code itself comprises a number of thin, parallel bars of varying thickness, which are typically printed on the outside of a package containing the item to be identified. In a typical printing operation, a printer is supplied with "master" Universal Product Code. This master is normally either a positive or negative of the desired code which is accurately reproduced on a transparent film. In a usual master Universal Product Code that is supplied to a printer, a certain amount of "bar width reduction" is built into this master. In other words, the bars on the master supplied to the printer are reduced in width, that is, they are thinner than would be required on a printed copy. The amount of bar width reduction depends on the particular printing operation; for example, the required reduction might depend on the extent the ink might be expected to spread during a particular printing operation. This bar width reduction is frequently in the range of about 0.003 inches per bar; it may be higher or lower, depending on the printer's requirements and techniques but the bar width reduction is always the same for each bar on a given code.
The dimensions of the printed code, in a direction perpendicular to the bars, is typically 11/2 inches. The height of the bars is typically 1 inch. This is what is called a code of "nominal" size. The code, however, may vary from 80 percent to 200 percent of nominal size without causing any problem with the optical scanner.
A serious problem occasionally arises when the optical scanner, for one reason or another, is unable to read a given code and "rejects" the item. This problem, when it occurs, is a great inconvenience in a retail grocery store, since a check-out clerk will be required to manually verify the price of the item rejected, and inventory data may lose its integrity. The problem has usually been caused by an inaccurate replication of the bar code during printing.
The inaccuracy that is most likely to occur, and which gives the most frequent problem with scanners, is an inaccurate replication of the width of each bar. Sometimes the code may be printed with one or more bars being thinner than they should, while at other times one or more bars may be wider than they should be. Whether or not a given code is printed correctly may depend on many factors that can be controlled during printing, such as the speed of printing, the temperature of the ink, the type and viscosity of the ink used, the printing pressure and related factors. And the accuracy of the printed Universal Product Code is only as good as the master symbol provided to the printer.
Because of the problem of rejecting or misreading items, industry has set standards for printed Universal Product Codes, which, hopefully, printers will be able to follow. It has been found that the width of the bars is crucial with respect to reading the code.
For a code of nominal size, that is 1".times.11/2", the printed bars may be wider or thinner than the ideal by an amount exceeding no more than approximately 0.0040 inch. For a code printed 80 percent of nominal size, the tolerance becomes smaller, that is about 0.0014 inch, while for a code printed 200 percent of nominal size, the tolerance can be as great as 0.010 inch. As mentioned above, the bars on a given code maay be of varying thickness, and the above tolerances are for all bars without regard to their thickness.
With respect to the master symbol that is supplied to the printer, a higher degree of accuracy is required. Manufacturers of master symbols typically produce masters with a .+-.0.0002 inch tolerance in the width of each bar. That is, a bar may be thicker or thinner than that amount as compared to an ideal bar. This very low tolerance is, unlike the tolerance permitted for a printed sample, not dependent upon the size of the Universal Product Code. The permitted tolerance is the same for a code of nominal size as for a code 200% of nominal size. Although the permitted tolerance is much less for master symbols than for printed Universal Product Codes, because master symbols are usually prepared more carefully and under more controlled conditions, the higher degree of accuracy is usually not as difficult to accomplish as when producing printed Universal Product Codes for use on actual products.
Reproducing printed Universal Product Codes to acceptable tolerances has presented a problem for the printing industry primarily because there is no rapid, inexpensive way for a printer to determine whether a printed code falls within acceptable levels of tolerance. Producing master symbols that are used for preparing printing plates of the required degree of accuracy is also a problem because there is no rapid way of determining whether the Universal Product Code bars on a master symbol are reproduced within the required very low tolerance.
Thus, there is a need in the field for an inexpensive apparatus and method that can be used to rapidly determine if a printed Universal Product Code falls within acceptable levels of tolerance. Most desirably, such an apparatus should be usable in a printing shop so that an operator can rapidly determine if a given code is within tolerance. If it is not, he maay of course desirably adjust his printing techniques to correct the problem.
There is also a need in the field for an inexpensive apparatus and method that can be used to determine if a master symbol Universal Product Code is reproduced with the required degree of accuracy. This apparatus and method should, of course, be capable of determining whether a given Universal Product Code bar on the master is reproduced to the required .+-.0.0002 inch accuracy.
It should be realized that, unlike other verification devices that provide the means for rejecting or accepting the bar code symbol by a scanner, this device is directed to determine if all bar widths fall within the specifications set for the particular symbol magnification in test.